In passenger transport vehicles, such as airplanes and trains, it is known to provide seats that are fitted with electric actuators. Each seat generally includes leg rest and a seat back that are movable relative to a seat proper. The leg rest and the seat back are hinged to respective ends of the seat proper, and each is associated with an electric actuator enabling it to move. The seat itself is sometimes movable as a whole relative to the deck or floor under the control of an actuator.
In order to avoid the leg rest or the seat back injuring a passenger while it is moving, or indeed in order to avoid damaging baggage placed on the track of the moving element, it is known to measure continuously the electric current being drawn by each actuator. If current consumption exceeds a predetermined threshold value, then the actuator is stopped immediately.
When a seat element controlled by an actuator encounters an obstacle, that element is stopped or braked. The electric motor of the actuator driving the element is then blocked, so the current drawn by the motor increases in very significant manner. Stopping the actuator whenever high current is detected in its motor serves to avoid damaging the seat or the obstacle it has encountered.
The current thresholds that lead to stopping are set at relatively high values in order to enable the actuator to be capable of operating while exerting a large force on the seat or the seat element during normal displacement.
Under certain circumstances, even when no obstacle is encountered, it is necessary for an actuator to be capable of producing a large force in order to move a moving element, in particular because of the way the seat is designed. This applies, for example, when a seat element needs to travel up a ramp while it is moving.
Thus, in certain circumstances, the protection provided by making use of a current threshold can be insufficient for providing effective protection to baggage, to the limb of a passenger, or to the seat itself.